Method for producing sulfonated aromatic polymers and use of the process products for producing membranes

ABSTRACT

A novel non-aggressive sulfonating process for aromatic polymers is described. 
     The process encompasses: 
     a). dissolving the aromatic polymer in a substantially anhydrous acid selected from the group consisting of concentrated sulfuric acid, chlorosulfonic acid, and oleum, 
     b) adding an organic solvent which is inert under the conditions of the reaction, 
     c) adding a carboxylic anhydride, 
     d) adding a sulfonating agent, and 
     e) carrying out the sulfonation at a temperature below  25 ° C. and for a time sufficient to achieve the desired degree of sulfonation. 
     The resultant homogeneous products of the process may preferably be used to produce membranes, for example for fuel cell applications

The present invention relates to a process for preparing sulfonatedaromatic polymers, in particular sulfonated aromatic polyether ketonesand sulfonated aromatic polyether sulfones, and also to the use of theproducts of the process for membrane production.

Aromatic sulfonated polymers are used in many applications, for examplein the form of membranes, these being used in fuel cells,high-performance capacitors, and dialysis devices.

Fuel cells are electrochemical energy converters which have particularlyhigh efficiency. Among the various types of fuel cells, polymerelectrolyte fuel cells have high power density and low weight to powerratio.

For further development of fuel cell technology, in particular for itsuse on a larger scale, the production costs of the materials used haveto be reduced, but this must not lead to any need to accept performancewhich is inferior to that of the materials used to date.

Polyether sulfones (hereinafter also termed “PES”) are commerciallyavailable products and have high resistance to heat, chemicals, andmechanical effects. A typical example of polyether sulfones is given inthe figure below.

The sulfonation of PES is of great interest for producing polymers whichcan be used in separation processes using membrane methods.

The prior art has disclosed various sulfonation processes for PES, forexample in EP-A-0,008,894; EP-A-0,112,724; U.S. Pat. No. 4,508,852; U.S.Pat. No. 3,709,841 and DE-A-3,814,760.

However, these previously disclosed sulfonation processes have manydisadvantages. For example, the use of strong sulfonating agents, suchas oleum or chlorosulfonic acid, at temperatures above 25° C. risksdegrading polymer chains. To avoid polymer degradation, therefore, thereaction temperature would have to be kept low. This in turn usuallyleads to a low degree of sulfonation, and also to long reaction times.Sulfonation by previously disclosed processes in organic solvents hasalso been found to proceed heterogeneously. This generally gives asulfonated product with inhomogeneous structure.

U.S. Pat. No. 4,508,852 describes other sulfonation processes for PES.In one of the processes, dichlorosulfonic acid is used as both solventand sulfonating agent. The temperature during the reaction is initiallyset at room temperature for 2 h and then to 82° C. for 30 min. A secondprocess uses 1,1,2,2-tetrachloroethane as solvent and chlorosulfonicacid as sulfonating agent. The sulfonation is carried out at 150° C.under a superatmospheric pressure generated by nitrogen. The thirdprocess suspends PES in 1,2-dichloroethane. The suspension becomes clearafter addition of chlorosulfonic acid. However, the sulfonated PESprecipitates during the course of the reaction. Sulfonation by theprocess therefore proceeds heterogeneously.

These three known processes likewise have many disadvantages. Forexample, it is impossible to avoid side-reactions and thereforeby-products (chlorosulfonated products) by using chlorosulfonic acid.The process is moreover difficult to control, since the high reactiontemperature permits only a relatively short reaction time. Thesulfonated PES moreover has low viscosity, which may be attributable topolymer chain degradation.

EP-A-0,008,894 and other references (cf. LÜHui-Juan; SHEN Lian-Chun;WANG Cai-Xia; JIANG Da-Zhen; CHEMICAL JOURNAL of CHINESE UNIVERSITIES;No. 5 Vol. 19; 05.1998; pp. 833-835) state that no sulfonation of PESoccurs in concentrated sulfuric acid. Sulfonation of PES inchlorosulfonic acid takes more than 20 h at room temperature. Theresultant product is water-soluble. The sulfonation of PES can likewisebe carried out in concentrated sulfuric acid by using oleum assulfonating agent “overnight”, the sulfonated PES being water-soluble.This may be attributable to the excessive degree of sulfonation and/orto polymer degradation. According to this prior art, controllablesulfonation is not possible using chlorosulfonic acid or oleum.

The same conclusion is found in EP-A-0,112,724. This prior art describesnovel sulfonation processes.

The process describes suspends PES in dichloromethane and treats it withsulfonating agents, e.g. SO₃ or chlorosulfonic acid, for a period of 4hours at a temperature of from 0 to 5° C.

U.S. Pat. No. 4,413,106 carries out the same sulfonation of PES usingoleum. However, the sulfonation is carried out heterogeneously, and thismay be the cause of structural inhomogeneity of the sulfonated PES.

DE-A-38 14 760 describes the sulfonation of PES in pure sulfuric acidusing 65% strength oleum. The PES sulfonated within a short time (3hours) and at a low temperature has a low degree of sulfonation (22%)and a reduced viscosity. Carrying out the reaction within a period of 22hours at 25° C. gives a 39% degree of sulfonation of the PES. If thetemperature is 40° C. the PES is degraded. However, no satisfactoryresult is obtained using the previously disclosed process when thetemperature is below 5° C.

An article by LüHui-Juan et al. in Chemical Journal of ChineseUniversities; No. 5 Vol. 19; 05.1998; pp. 833-835 describes the kineticsof sulfonation reactions. From this it is apparent that the sulfonationrate in concentrated sulfuric acid when using chlorosulfonic acid isvery low within the first 10 hours. In contrast, the sulfonation rate indichloromethane is very high even at the start of the reaction.

There continues to be a requirement for processes which can be carriedout cost-effectively for the sulfonation of aromatic polymers. Aparticular issue is whether sulfonation can be carried out within ashort period and at a low temperature, without polymer chaindegradation. Sulfonation should also be controllable and the degree ofsulfonation should be variable.

WO-A-96/29,359 and WO-A-96/29,360 describe polymer electrolytes madefrom sulfonated aromatic polyether ketones and the production ofmembranes from these materials.

EP-A-0 152 161 describes polyether ketones (hereinafter termed “PEK”)mainly composed of the repeat units —O—Ar—CO—Ar— (Ar=divalent aromaticradical), and shaped structures produced from these.

J. Polym. Sci.: Vol. 23, 2205-2222, 1985 describes sulfonated, strictlyalternating polyether ketones with the repeat unit —O—Ar—CO—Ar—. Here,the polyether ketone synthesis uses electrophilic attack rather thannucleophilic attack as described in EP-A-0 152 161. The polymers weresulfonated by sulfur trioxide using triethyl phosphate indichloroethane. Another sulfonation method used in this reference ischlorosulfonation using chlorosulfonic acid. However, molecular weightdegradation is again observed with this method, depending on the degreeof sulfonation. Amidation of the acid chloride follows.

Starting from this prior art, the object on which the present inventionis based is therefore to provide a simple and cost-effective processwhich sulforiates aromatic polymers and which minimizes degradation ofthe polymer during sulfonation, and which can be carried out in ahomogeneous phase, and which maximizes product homogeneity.

The present invention provides a process for preparing sulfonatedaromatic polymers, encompassing:

a) dissolving the aromatic polymer in a substantially anhydrous acidselected from the group consisting of concentrated sulfuric acid,chlorosulfonic acid, and oleum,

b) adding an organic solvent which is inert under the conditions of thereaction,

c) adding a carboxylic anhydride,

d) adding a sulfonating agent, and

e) carrying out the sulfonation at a temperature below 25° C. and for atime sufficient to achieve the desired degree of sulfonation.

The sequence of steps b) to d) of the process may be as desired. Thesesteps may also be undertaken simultaneously.

The aromatic polymer used in step a) may be any polymer whose mainpolymer chain has sulfonatable aromatic groups and which is soluble inthe solvents used in step a). Examples of these are aromatic polyamides,aromatic polyimides, aromatic polyether ketones (in the widest sense,i.e. polymers having ether bridges and ketone bridges in the mainpolymer chain), aromatic polycarbonates, aromatic polysulfones,polysulfoxides, or polysulfides, aromatic polyether sulfones, aromaticpolyesters. Particular preference is given to aromatic polyetherketones, polyether ether ketone, polyether ether sulfone, and inparticular polyether sulfones.

The substantially anhydrous acid used in step a) usually has watercontent of less than 3% by weight, preferably less than 2% by weight, inparticular less than 1.5% by weight. The acids may be used individuallyor in combination.

The concentration of the dissolved aromatic polymer in the substantiallyanhydrous acid is usually from 0.01 to 30% by weight, preferably from0.1 to 25% by weight, in particular from 1 to 20% by weight, based onthe solution.

The inert organic solvent used in step b) may be a hydrocarbon,preferably halogenated, particularly preferably an aliphatic chlorinatedand/or fluorinated hydrocarbon. This is usually liquid under theconditions of the reaction. The amount selected is such as to produce ahomogeneous solution.

Examples of hydrocarbons are saturated aliphatic hydrocarbons liquid at25°C., in particular branched or unbranched hydrocarbons having from 5to 15 carbon atoms, for example pentane, hexane, heptane, octane, ordecane, or ethylenically unsaturated aliphatic hydrocarbons, inparticular having from 5 to 15 carbon atoms, for example hexene, octene,or decene.

Examples of halogenated hydrocarbons are chlorinated and/or fluorinatedsaturated aliphatic hydrocarbons liquid at 25° C., for example mono-,dl-, tri-,

or tetrachloromethane, mono-, dl-, tri-, tetra-, penta-, orhexachloroethane, or the various chloro/fluoromethanes orchloro/fluoroethanes. Dichloromethane is particularly preferred.

The carboxylic anhydride used in step c) may be of any desired type. Usemay be made not only of linear anhydrides but also of cyclic compounds.

Examples of these are anhydrides of aliphatic monocarboxylic acids, suchas formic, acetic, propionic, butyric, and caproic acid, anhydrides ofaliphatic or ethylenically unsaturated aliphatic dicarboxylic acids,such as malonic acid, succinic acid, or lactic acid, anhydrides ofcycloaliphatic carboxylic acids, such as cyclohexanecarboxylic acid,anhydrides of aromatic mono- or dicarboxylic acids, such as benzoicacid, phthalic acid, isophthalic acid, or terephthalic acid. Besidesthese, use may also be made of anhydrides of different carboxylic acids.It is also possible to use trifluoroacetic anhydride (CF₃CO)₂O ortrichloroacetic anhydride (CCI₃CO)₂O. Acetic anhydride andtrifluoroacetic anhydride are particularly preferred.

The sulfonating agent used in step d) may be any desired sulfonatingagent as long as this is capable of sulfonating the aromatic main chainof the polymer under the conditions of the reaction. Examples of theseare oleum, concentrated sulfuric acid, chlorosulfonic acid.

Preference is given to chlorosulfonic acid or oleum, in particular 20%strength oleum.

The sulfonation reaction is preferably carried out at temperatures below10° C., in particular at temperatures below 5° C., particularlypreferably at from 0 to 5° C. The lower limit may also be below 0° C. aslong as the mixture remains liquid and can be stirred.

The usual period of time for which the sulfonation reaction is carriedout is less than 15 hours. The sulfonation preferably takes less than 10hours and very particularly preferably less than 6 hours.

The process of the invention is characterized by a low reactiontemperature and short reaction time. The sulfonated aromatic polymersprepared by this process, in particular the polyether sulfones, havedegrees of sulfonation which are particularly high and can be varied,and there is no significant polymer chain degradation.

The homogeneity of the sulfonation makes the products of the processparticularly suitable for producing membranes for applications in whicha high level of uniformity of properties is important. Examples of theseare electrochemical applications, such as electrodialysis, or use infuel cells, or use as a dielectric, for example in high-capacitancecapacitors.

This invention also provides the use of the sulfonated aromatic polymersobtainable by the process of the invention, in particular of thesulfonated aromatic polyether sulfones, for producing homogeneousmembranes or blend membranes.

FIGS. 1 and 2 illustrate the sulfonation process of the inventiondiagrammatically, using PES as example.

While there is no intention to be bound by descriptions of themechanism, it is assumed that the anhydride activates the sulfonatingagent.

The activated sulfonating agent then reacts with the aromatic polymervia electrophilic substitution as in the diagram below (see FIG. 2).

In the course of the process as shown in FIG. 2 an anhydrous acid isproduced by dropwise addition of sulfonating agent, such aschlorosulfonic acid or oleum, into 95˜97% strength sulfuric acid. PESthen dissolves at 0° C. in the anhydrous acid. An inert organic solvent,such as dichloromethane (“DCM”), is then admixed. The sulfonating agent,such as chlorosulfonic acid and/or oleum, is then added. Finally, theactivating agent acetic anhydride is added. The sulfonation may proceedat a temperature of from 0 to 10° C. and may be terminated by pouringthe reaction mixture into water.

In another version of the process of the invention, an anhydrous acid isagain first prepared by dropwise addition of sulfonating agent, such aschlorosulfonic acid or oleum, into 95-97% strength sulfuric acid. PES isthen dissolved in the anhydrous acid at 0° C. Chlorosulfonic acid oroleum is then added as sulfonating agent. Acetic anhydride activatingagent is then added in dichloromethane. The sulfonation may proceed at atemperature of from 0 to 10° C. and may be terminated by pouring thereaction mixture into water.

The amount of chlorosulfonic acid or oleum used during preparation ofthe anhydrous acid is related to the water content in the sulfuric acid.The amount used of the sulfonating agent, and also of the activatingagent (“quasi-catalyst”) is related to the targeted degree ofsulfonation. The reaction time should accordingly be limited to a periodof up to 6 hours.

The aromatic polyether sulfones sulfonated by the process of theinvention were studied with the aid of FTIR, NMR, titration, GPC, andelemental analysis, and also DSC. Surprisingly, this showed that theprocesses permit controllable sulfonation of PES at low temperature andwithin a short reaction time.

Membranes were also produced from sulfonated PES, or blend membranesfrom sulfonated PES and unmodified PES; from sulfonated PES and aminatedPES, and also from sulfonated PES and polybenzimidazole, PBI. To producethe membrane, N,N-dimethylacetamide (DMAC) or N-methylpyrrolidone (NMP)was used as solvent, and a polymer solution was prepared by dissolvingsulfonated PES, and also other blend components, in solvent. A doctorwas used to spread a film of the polymer solution on a substrate, andthe solution was evaporated to produce the membrane. The examples belowillustrate, but do not limit, the invention.

EXAMPLE 1

100 ml of 95-97% strength sulfuric acid formed an initial charge andwere treated with 35 ml of chlorosulfonic acid at 0° C. 20 g of PES(grade E6020; BASF AG) were then dissolved in the mixture at 0° C. 50 mlof dichloromethane were then admixed. The solution was cooled to 0° C.,with stirring. Within 30 minutes, 4 ml of chlorosulfonic acid were addeddropwise to the polymer solution. 8 ml of acetic anhydride were thenadded. The sulfonation then proceeded for 3.3 hours at from 5 to 10° C.

Table 1 lists the GPC data for unmodified PES and sulfonated PES.

TABLE 1 GPC data Sulfonated PES Unmodified PES Mn 1.512E+4 g/mol4.554E+3 g/mol Mw 4.033E+4 g/mol 4.152E+4 g/mol Mz 6.992E+4 g/mol7.286E+4 g/mol Mv 3.675E+4 g/mol 3.744E+4 g/mol D* 2.668E+0 9.117E+0

Measurement conditions: DMSO; 4.3 g/I; PS acid; 60° C.; 1.0 ml/min;D*=polydispersity

Table 1 shows that the average molar mass of sulfonated PES is higherthan that of the unmodified PES, this being attributable to the sulfonegroups in the underlying polymer. Mw, Mz, and Mv are comparable forsulfonated PES and unmodified PES.

Table 2 lists the calculated and measured values for elemental analysison sulfonated PES.

TABLE 2 Results of elemental analysis and titration Element Calculated1* (%) Calculated 2** (%) Found*** C% 55.8 54.5 52.5 H% 2.8 2.8 2.5 O%24.8 25.6 27.7 S% 16.5 17.1 16.5 Cl% <0.04 *Values calculated fromsulfur content, determined with the aid of elemental analysis. **Valuescalculated from sulfur content, determined with the aid of titration.***Values determined with the aid of elemental analysis.

The results from GPC and elemental analysis show that no polymer chaindegradation takes place during sulfonation using the abovementionedprocesses.

FIG. 3 shows the FTIR spectrum of sulfonated PES.

As described in the references [Lü Hui-Juan et al. in Chemical Journalof Chinese Universities, No. 5 Vol. 19, 051/998. pp. 833-835; In-CheolKim et al. in Membrane Journal; Vol. 8. No. 4, 12/1998, pp. 210-219; R.Nolte et al. in Journal of Membrane Science (1993) 211-220], the newabsorption bands at 1028 cm⁻¹, 737 cm⁻¹ and 1465 cm⁻¹ derive from theSO₃H groups on the aromatic rings relative to ortho-ether bridges.

FIG. 4 shows the ¹H-NMR spectrum of sulfonated PES.

As described in the abovementioned references, the chemical shift at8.31 ppm arises from sulfonation of PES.

The degree of sulfonation or ion exchange capacity (“IEC”) wasdetermined as a function of reaction time by potentiometric titration.

From FIG. 5, the degree of sulfonation of the sulfonated PES is seen tobe a function of reaction time, a degree of sulfonation of 41.2%(IEC=1.55 meq/g) being achieved within a period of 5 hours.

The reaction time is considerably shortened over the process disclosedin DE-A-38 14 760 (see Examples 1-3), and the reaction temperature islower, while the degree of sulfonation of the sulfonated PES isincreased.

EXAMPLE 2

100 ml of 95-97% strength sulfuric acid formed an initial charge at roomtemperature and were treated with 110 ml of 20% strength oleum. Thetemperature of the solution was then lowered to 0° C. 40 g of PES (gradeE7020; BASF AG) were then dissolved in the mixture at 0° C. 100 ml ofdichloromethane were then admixed. 20 ml of 20% strength oleum wereadded to the polymer solution dropwise within a period of 30 min.Finally, 8 ml of acetic anhydride were added. The sulfonation thenproceeded for 2 hours at from 0 to 10° C. The total time of the processfrom dissolving the PES to the end of sulfonation was about 5 hours.

From FIG. 6 it is seen that acceleration of the sulfonation occurredonly after addition of acetic anhydride.

Analogous characterization results to those in Example 1 were obtainedfrom FTIR and NMR. The degree of sulfonation of the product determinedby titration was 34.3% (IEC=1.32). Compared with the previouslydisclosed process from DE-A-38 14 760 (see Example 3) the reaction timewas similar and the reaction temperature lower (25° C. in the DE-A) toachieve a comparable degree of sulfonation. At similar reaction time andtemperature the degree of sulfonation is considerably higher than thatin DE-A-38 14 760 (cf. Examples 1 and 2).

EXAMPLE 3

200 ml of 95-97% strength sulfuric acid formed an initial charge at 10°C. and were treated with 220 ml of 20% strength oleum. 80 g of PES(grade E7020; BASF AG) were then dissolved in the mixture at 10° C. 16ml of chlorosulfonic acid were added dropwise to the polymer solutionwithin a period of 30 min. Finally, 18 ml of acetic anhydride were addedin 100 ml of dichloromethane. The sulfonation then proceeded for 4 hoursat 10° C.

The titration result showed the degree of sulfonation of the product tobe 96% (IEC=3.1 meq/g). The product was water-soluble.

EXAMPLE 4

200 ml of 95-97% strength sulfuric acid formed an initial charge at 10°C. and were treated with 129 ml of 20% strength oleum. 70 g of PES(grade E7020; BASF AG) were then dissolved in the mixture at 10° C. 14ml of chlorosulfonic acid were added dropwise to the polymer solutionwithin a period of 30 min. Finally, 15 ml of acetic anhydride were addedin 100 ml of dichloromethane. The sulfonation then proceeded for 2 hoursat 10° C.

The titration result showed the degree of sulfonation of the product tobe 13% (IEC=0.54 meq/g).

EXAMPLE 5 (MEMBRANE PRODUCTION)

Tables 3 and 4 give an overview of the membranes produced.

TABLE 3 Membrane production Solvent NMP Polymer components SulfonatedPES or sulfonated PES/PES Polymer concentration 20-25% Evaporationtemperature 90-120° C. Residence time in oven 20 h Post-treatment ofmembranes 1 N H₂SO₄, at 40° C. demineralized water at 40° C.

TABLE 4 Data for membranes produced Modu- Elon- Mem- Swe Cond. lus ofgation brane IEC (% by (mS/ elasticity at break No. Materials (meq/g)weight)* cm)* (N/mm²)* (%)* TE-46 Sulfonated 1.35 34 106.4 138.3 150.5PES TE-47 Sulfonated 1.3 44.6 154.4 183.9 111.9 PES and 10% PES

Measurement carried out in demineralized water at 80° C. Sw indicatesmembrane swelling. Cond indicates membrane conductivity.

What is claimed is:
 1. A process for preparing sulfonated aromaticpolymers, encompassing: (a) dissolving the aromatic polymer in asubstantially anhydrous acid selected from the group consisting ofconcentrated sulfuric acid, chlorosulfonic acid, and oleum, (b) addingan organic solvent which is inert under the conditions of the reaction,(c) adding a carboxylic anhydride, (d) adding a sulfonating agent, and(e) carrying out the sulfonation at a temperature below 25° C. and for atime sufficient to achieve the desired degree of sulfonation.
 2. Theprocess as claimed in claim 1, wherein the organic solvent inert underthe conditions of the reaction is selected from the group consisting ofaliphatic hydrocarbons liquid at 25° C., in particular branched orunbranched hydrocarbons having from 5 to 15 carbon atoms, andchlorinated and/or fluorinated aliphatic hydrocarbons liquid at 25° C.,in particular dichloromethane.
 3. The process as claimed in claim 1,wherein the carboxylic anhydride is selected from the group consistingof anhydrides of aliphatic monocarboxylic acids, anhydrides of aliphaticor ethylenically unsaturated aliphatic dicarboxylic acids, anhydrides ofcycloaliphatic carboxylic acids, and anhydrides of aromatic mono- ordicarboxylic acids, in particular acetic anhydride and triflouroaceticanhydride.
 4. The process as claimed in claim 1, wherein the sulfonatingagent is selected from the group consisting of oleum and chlorosulfonicacid.
 5. The process as claimed in claim 1, wherein the temperatureduring the entire reaction time, and in particular during thesulfonation, is set to be below 10° C., in particular below 5° C.
 6. Theprocess as claimed in claim 1, wherein the reaction takes less than 6hours.
 7. The process as claimed in claim 1, wherein the aromaticpolymer is dissolved in anhydrous acid and the concentration of thispolymer solution is in the range from 0.01 to 30% by weight, based onthe solution.
 8. The process as claimed in claim 1, whereindichloromethane is used as solvent and acetic anhydride ortrifluoroacetic anhydride as anhydride.
 9. The process as claimed inclaim 1, wherein at the end of the sulfonation the sulfonated aromaticpolymer is stirred into iced water at a temperature below 5° C.
 10. Theprocess as claimed in claim 1, wherein 20% strength oleum and/orchlorosulfonic acid with purity above 97% are used as sulfonating agent.11. The process as claimed in claim 1, wherein polyether sulfones, suchas PES or PEES, or polyketones, such as PEK, PEEK, PEKEK, PEKK, orPEEKK, are used as aromatic polymer.
 12. Homogeneous membranes or blendmembranes made from two or more components, where said components areselected from the group consisting of: sulfonated polyether sulfone,unmodified polyether sulfone, sulfonated polyether sulfone, aminatedpolyether sulfone, sulfonated polyether sulfone, polybenzimidazole andcombinations thereof, where sulfonated aromatic polymers are made by aprocess of: (a) dissolving the aromatic polymer in a substantiallyanhydrous acid selected from the group consisting of concentratedsulfuric acid, chlorosulfonic acid, and oleum, (b) adding an organicsolvent which is inert under the conditions of the reaction, (c) addinga carboxylic anhydride, (d) adding a sulfonating agent, and (e) carryingout the sulfonation at a temperature below 25° C. and for a timesufficient to achieve the desired degree of sulfonation.
 13. A fuel cellwhich comprises a membrane, where said membrane is made by the processof claim
 12. 14. A multilayer membrane comprising at least two membraneswhere at least one of said membranes is fabricated from a sulfonatedaromatic polymer, where said sulfonated aromatic polymer is produced bythe steps of: (a) dissolving the aromatic polymer in a substantiallyanhydrous acid selected from the group consisting of concentratedsulfuric acid, chlorosulfonic acid, and oleum, (b) adding an organicsolvent which is inert under the conditions of the reaction, (c) addinga carboxylic anhydride, (d) adding a sulfonating agent, and (e) carryingout the sulfonation at a temperature below 25° C. and for a timesufficient to achieve the desired degree of sulfonation.
 15. Anelectrical membrane process comprising the step of: providing a membranemade by the process of claim 12, where said electrical membrane processis used for electrodialysis.